Carbon nanostructure preblends and their applications

ABSTRACT

A method for preparing a “preblend” of nano-structured carbon, such as nanotubes, fullerenes, or graphene, and a particulate solid, such as carbon black, graphitic particles or glassy carbon involving wet-mixing and followed by optional drying to remove the liquid medium. The preblend may be in the form of a core-shell powder material with the nano-structured carbon as the shell on the particulate solid core. The preblend may provide particularly improved dispersion of single-wall nanotubes in ethylene-α-olefin elastomer compositions, resulting in improved reinforcement from the nanotubes. The improved elastomer compositions may show simultaneous improvement in both modulus and in elongation at break. The elastomer compositions may be formed into useful rubber articles.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to methods of dispersing carbonnanostructures such as nanotubes in polymers, for example to makeelastomer compositions, methods for forming carbon nanostructurepreblends for the same, and applications of the resulting preblends andcompositions.

2. Description of the Prior Art

Because carbon nanotubes (“CNT”) are produced as entangled bundles offibers, getting them to disperse in a polymer is a critical step intheir utilization as reinforcing additives. A number of approaches havebeen used to obtain polymers with dispersed carbon nanotubes. Amongthese methods are melt blending of CNT into thermoplastic resins,polymerization in the presence of the CNT, high shear mixing, chemicalmodification of the CNT, and the use of surfactants.

Regarding mixing carbon nanotubes into rubber or elastomeric polymers,it is very difficult to disperse the CNT in a matrix material with ashigh a viscosity as most elastomers or rubbers have. The application ofheat does not reduce the viscosity of the polymer significantly enoughas it does in melt-blending into plastics. What is needed is a method toimprove the dispersibility of the CNT in rubber.

U.S. Pat. No. 7,785,701 B2 discloses a carbon fiber composite materialcomprising an elastomer and a carbon nanofiber dispersed in theelastomer, wherein the elastomer has an unsaturated bond or a group,having affinity to the carbon nanofiber. When the affinity of theelastomer for the nanofiber is high, the dispersion is reportedly easyby the shear force of mixing, e.g. on an open roll mill. Dispersion isreportedly not so easy for nonpolar elastomers such as EPDM. Theresulting mill-mixed compositions show an increase in modulus andstrength but a decrease in elongation as is typical of many reinforcingfillers, relative to the composition without nanofiber.

EP 2,138,535 B1 discloses a vulcanizable composition containing aspecific hydrogenated carboxylated nitrile rubber (HXNBR), across-linking agent and carbon nanotubes and a process for preparingsuch compositions. It is reported therein that solvent mixing, meltmixing and the spray drying process have been employed as processingmethods to prepare some rubber/CNT composites. The examples ofmulti-wall carbon nanotubes (“MWCNT”) in HXNBR were conventionally mixedin an internal mixer and two-roll mill. The resulting compositionsshowed an increase in modulus and strength but essentially the sameelongation.

Reference is made to Applicant's co-pending U.S. patent application Ser.No. 14/243,634 filed Apr. 2, 2014, titled Method for Rubber ReinforcedWith Carbon Nanotubes.

SUMMARY

The present invention is directed to improved methods of dispersingcarbon nanostructures, such as nanotubes, in elastomers through theformation of preblend compositions containing carbon nanostructures andthe resulting elastomer compositions and articles made therefrom.

By suspending or dissolving the CNT, or other carbon nanostructuredmaterial, in a solvent and blending with carrier particles such ascarbon black followed by drying, it is possible to disperse the CNT inand around the carrier particles, or to disperse the carrier particlesthroughout the CNT network. It has been discovered that such a preblendhelps the CNT disperse in rubber, especially nonpolar elastomers such asethylene-alpha-olefin elastomers. As a result, improvements in modulus,elongation and tear can be realized. The fact that the CNT can increasemodulus while simultaneously increasing elongation at break and tearproperties is believed to be a new and advantageous result. The use ofcarbon black as the carrier particulate solid may be readilyincorporated into existing rubber processes and may be cost effective.

The invention is directed to a method including the steps of forming acarbon preblend by dispersing carbon nanostructures in a liquid medium,mixing with a particulate solid, such as carbon black, and drying toremove the liquid, resulting in a preblend of nanostructures and theparticles, for example a preblend of CNT and carbon black. The preblendmay then be dispersed in a polymer matrix, such as an elastomer matrix.The invention is also directed to the resulting polymer or elastomer orrubber composition and to articles made from the composition, such astires, power transmission belts, transport belting, or hose.

The inventive method may include suspending or dissolving both CNT andcarrier particles such as carbon black in a solvent, mixing and finallydrying them. The inventive method can lead to inventive CNT-coatedparticles or particles coated with other carbon nanostructured materialsto form a preblend

Depending on dimensions and amounts of both the CNT and the carrierparticles, instead of CNT-coated particles, a structure consisting of aCNT network in which particles are dispersed can be formed.

A CNT/carbon black preblend may provide particularly improved dispersionof single-wall carbon nanotubes (“SWCNT”) in an ethylene-alpha-olefinrubber composition, resulting in improved reinforcement from the SWCNT.

The amount of CNT or other nanostructured carbon in the elastomercompositions of the invention may be from 0.5, 1, or 2 weight % up to 2,3, 4, or 5 weight %. The amount of CNT in the preblend may be from 1%,or 5%, or 7% up to about 20%, or up to 30%, or up to 50% by weight basedon the weight of the preblend.

The inventive elastomer compositions may be formed into useful rubberarticles, such as tires, belts, hose, or vibration control components.Power transmission belts include V-belts, multi-v-ribbed belts,synchronous belts, flat belts, and the like, without limit.

The improved elastomer compositions containing some amount of the CNTpreblend may show simultaneous improvement in both modulus and inelongation at break. The compositions may also show improvements in tearstrength, cut or crack growth rates and fatigue resistance.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures for carrying out the samepurposes of the present invention. It should also be realized by thoseskilled in the art that such equivalent constructions do not depart fromthe scope of the invention as set forth in the appended claims. Thenovel features which are believed to be characteristic of the invention,both as to its organization and method of operation, together withfurther objects and advantages will be better understood from thefollowing description when considered in connection with theaccompanying figures. It is to be expressly understood, however, thateach of the figures is provided for the purpose of illustration anddescription only and is not intended as a definition of the limits ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form part ofthe specification in which like numerals designate like parts,illustrate embodiments of the present invention and together with thedescription, serve to explain the principles of the invention.

FIG. 1 is a flow chart of an embodiment of the inventive method.

FIG. 2 is a Raman spectrum measured at 785 nm of preblend materialconsisting of N550 carbon black and SWCNT in a 13:1 ratio mixed inethanol.

FIG. 3A is a Scanning Electron Microscopy (SEM) image of preblendmaterial consisting of N550 carbon black and SWCNT in a 13:1 ratio mixedin ethanol followed by filtration and drying overnight at 60° C.magnified by: ×2,500;

FIG. 3B is an SEM of the material of FIG. 3A magnified by: ×35,000;

FIG. 3C is an SEM of the material of FIG. 3A magnified by: ×120,000; and

FIG. 3D is another SEM of the material of FIG. 3A magnified by: ×120,000according to an embodiment of the invention.

FIG. 4 is an SEM of polymer beads coated with single-walled carbonnanotubes according to an embodiment of the invention.

FIG. 5 is an FE-SEM image of a control rubber compound with amagnification of ×35,000, with carbon black only added to rubber;

FIG. 6 is an FE-SEM image of a control rubber compound with amagnification of ×35,000 made by separate addition to rubber of N550carbon black and SWCNT; and

FIG. 7 is an FE-SEM image of a rubber compound with a magnification of×35,000 with N550 carbon black/SWCNT preblend wet-mixed in ethanol andadded to rubber according to an embodiment of the invention.

FIG. 8 is an SEM image of a carbon black/SWCNT preblend prepared bymixing in o-dichlorobenzene: N220 carbon black/SWCNT (5:1), magnified×40,000;

FIG. 9 is an SEM image of a carbon black/SWCNT preblend prepared bymixing in o-dichlorobenzene: N220 carbon black/SWCNT (7:1), magnified×40,000;

FIG. 10A is an SEM image of a carbon black/SWCNT preblend prepared bymixing in o-dichlorobenzene: N550 carbon black/SWCNT (5:1): magnified×25,000;

FIG. 10B is an SEM image of the preblend of FIG. 10A magnified ×70,000;

FIG. 11A is an SEM image of a carbon black/SWCNT preblend prepared bymixing in o-dichlorobenzene: N550 carbon black/SWCNT (7:1): magnified×25,000; and

FIG. 11B is an SEM image of the preblend of FIG. 11A magnified ×70,000.

DETAILED DESCRIPTION

The methods and elastomer compositions according to the inventioninclude a method for forming a preblend of carbon nanostructures, suchas CNT, with a particulate solid, such as carbon black and furthermethods for the dispersion of the prebelends in elastomers. Carbonnanostructures are carbon-based materials in which at least onedimension is on the order of less than one to several nanometers. Theyinclude but are not limited to structured nanocarbons such assingle-walled, double-walled, few-walled or multi-walled carbonnanotubes, graphene, few-walled graphenes, graphene oxides, fullerenicand forms of structured carbons and their chemical derivatives. Theyinclude fullerene molecules such as C60, C70, C84, etc., and fullerenemolecules containing another atom or atoms inside or outside thefullerene cage or one or more functional groups. Other carbonnanostructures include spheroids or spherules of carbon made up ofcurved carbon sheets or layers which have substantial fullereniccharacter. Fullerenic character is noted by the presence amongsix-member and sometimes seven member rings of five-membered carbonrings which result in curved sheets of carbon. Chemical derivatives ofcarbon nanostructures include any of the carbon-based materialsdescribed above that are functionalized, i.e. have added groups, e.g. byaddition reactions. Also, carbon nanostructures include structuredfragments of any of the structured nanocarbons described above. Apreblend is a mixture of materials made in advance of another mixingprocess, e.g. a rubber composition mixing process. The preblend isaccordingly mixed into an elastomer together with other desiredingredients to make an elastomer composition suitable for molding usefulelastomeric articles. FIG. 1 shows a flow chart of the method accordingto an embodiment of the invention. Preblends are also sometimes referredto as “predispersions” or simply “blends.”

In FIG. 1, method 100 includes the steps of blending 112, mixing 120,and making an article 124. The blending step 112 includes as inputscarrier particles 102 such as carbon black, carbon nanotubes 104,carrier liquid medium 106 and optionally other additives 105. The wetblending 112 step may include various orders of addition and/or mixing.In one preferred embodiment, CNT 104 is dispersed in liquid medium 106first, followed by addition of particulate solid 102. In anotherembodiment, CNT 104 and particulate solid 106 are each dispersed inseparate liquid media 106, and then the two dispersions are combined.The wet blending 112 is followed by drying 118. After the blending anddrying steps, the resulting CNT preblend 119 may be introduced intomixing step 120 along with desired polymer or rubber ingredients 122 toobtain a rubber compound suitable for making article 124. Mixing step120 may optionally include multiple mixing process steps and/or multipleingredient additions. In other embodiments, CNT in FIG. 1 may bereplaced by some other carbon nanostructure as defined above or mixturesthereof.

The carbon nanotubes (CNT) are very strong molecular fibers with smalldimensions across the fiber and reasonably large L/D ratios. Severalsynthetic methods are possible, with chemical vapor deposition (CVD),electric arc discharge (EAD) and combustion, as disclosed, e.g., in U.S.Pat. No. 7,887,775 and U.S. Pat. No. 7,396,520, among the more commonmethods used. The dimensions depend on the manufacturing process.Single-walled carbon nanotubes (SWCNT) may range from 0.5 to 6nanometers (nm) in diameter have lengths ranging from 0.1 to 5 microns(μm) in length, preferably 0.5 to 5 μm in length. A single-wall carbonnanotube is formed from a single graphene sheet folded into a cylinder.Multi-walled carbon nanotubes (MWCNT) range from 2 to 110 nm in diameterand from 0.1 to 1000 μm, preferably from 0.1 to 50 μm in length, andconsist of multiple layers of graphene rolled up on themselves to form atube shape. These dimensional variations depend on the process andmanufacturer. Either single-wall carbon nanotubes or multi-wall carbonnanotubes may be used in the inventive methods and compositions, butsingle-wall carbon nanotubes are preferred.

The carbon nanotube preblend comprises carbon nanotubes and aparticulate solid such as carbon black. Particulate solids of particularusefulness are those commonly used as reinforcing fillers ornon-reinforcing fillers in polymer or elastomer compositions, includingsilica, carbon black, clay, whiting, various metal oxides andhydroxides, and the like. Carbon black is preferred because of itswidespread use in rubber and its chemical compatibility with carbonnanotubes. Types of carbon black suitable for use in the present methodinclude those identified in ASTM D1765. Two suitable examples, as willbe seen below, include N550 and N220.

The amount of CNT in the preblend may be from 1%, or 5%, or 7% up toabout 50%, or up to 30%, or up to 20% by weight based on the weight ofthe preblend. The amount of CNT in the preblend may be expressed as aratio of particles to carbon nanotubes, and the ratio may be from about4:1 to 99:1 or to 20:1 by weight, or from 6:1 to 15:1, or about 9:1 toabout 14:1. The CNT may be readily blended with carbon black accordingto the methods described herein, and a CNT/carbon black preblend is verycompatible with ethylene-alpha-olefin elastomers such as EPDM.

The term “carrier liquid” or “liquid medium” refers to a liquid in whichcarbon nanotubes may be dissolved, dispersed or suspended. The carrierliquid may be removed by evaporation or drying, leaving the nanotubescoated on or intermixed with the carbon black. Suitable carrier liquidsinclude water or organic solvents including alcohols, chlorinatedaliphatic or aromatic solvents, ketones, other oxygen-containing orhalogen-containing hydrocarbon liquids. substituted aromatic molecules,alkyl substituted aromatics, halogenated substituted molecules,halogenated alkanes, partially hydrogenated aromatics, alkylamines,cyclic ethers, o-dichlorobenzene, toluene, xylene, benzene,dimethylformamide (“DMF”), ethylene chloride, chloroform,1,2,4-trimethylbenzene, 1,2,3,4-tetramethylbenzene, tetrahydrofuran,1,2-dibromobenzene, 1,1,2,2-tetrachloroethane,1,2,3,4-tetrahydronapthalene, octadecylamine, acetone. Other liquidswhich can be used include systems based, e.g., on water stabilized bymeans of surfactant with such surfactant being at least one memberselected from the group consisting of sodium cholate, (“NaDDBS”;C₁₂H₂₅C₆H₄SO₃Na), sodium octylbenzene sulfonate (NaOBS; C₈H₁₇C₆H₄SO₃Na),sodium butylbenzene sulfonate (“NaBBS”; C₄H₉C₆H₄SO₃Na), sodium benzoate(C₆H₅CO₂Na), sodium dodecyl sulfate (“SDS”; CH₃ (CH₂)₁₁—OSO₃Na), Triton(trademark of Dow Chemical Co.) X-100 (“TX100”;C₈H₁₇C₆H₄(OCH₂CH₂)_(n)—OH; n˜10), dodecyltrimethylammonium bromide(“DTAB”; CH₃(CH₂)₁₁N(CH₃)₃Br), dextrin, and polystyrene-polyethyleneoxide diblock copolymer (“PS-PEO”). Other non-ionic dispersal aids suchas outlined, e.g., in International Appl. No. PCT/US2010/045391 and U.S.patent application Ser. No. 13/725,080, can be used in water orsolvent-based systems. Temperature adjustments can also be used in wateror solvent-based systems in order to enhance the dispersion or solutionproperties. Two suitable examples, as will be seen below, includeethanol and o-dichlorobenzene.

The term polymer includes thermoplastic, elastomeric and thermosetpolymeric materials. The terms rubber and elastomer may be used somewhatinterchangeably, but rubber generally implies a crosslinked elastomermaterial, while some elastomers may in general be thermoplastic or maybe crosslinked. The terms “rubber” and “elastomer” are used herein torefer to the elastomeric or rubbery polymer which forms a primaryelastomeric constituent of an elastomeric or rubbery material, while theterms “rubber composition” and “elastomer composition” are used to referto a mixture of a primary elastomeric constituent with one or more othercompounding ingredients, such as fillers, fibers, antidegradants,process aids, curatives, cure accelerators, coagents, softeners,extenders, and the like. Any suitable elastomer may be used, includingwithout limit, natural rubber (NR), epoxidized natural rubber (ENR),isoprene rubber (IR), styrene-butadiene rubber (SBR), nitrile rubber(NBR), hydrogenated nitrile (HNBR), chloroprene rubber (CR),ethylene-α-olefin elastomers such as ethylene propylene rubber (EPM orEPDM), ethylene butene (EBM) or ethylene octene (EOM), butyl rubber(IIR), chlorobutyl rubber (CIIR), acrylic rubber (ACM), silicone rubber(Q), fluorine rubber (FKM), butadiene rubber (BR), epoxidized butadienerubber (EBR), epichlorohydrin rubber (ECO), cast urethane elastomers(PU), or polysulfide rubber (T); a thermoplastic elastomer such as anolefin-based elastomer (TPO), a polyvinyl chloride-based elastomer(TPVC), a polyester-based elastomer (TPEE), a polyurethane-basedelastomer (TPU), a polyamide-based elastomer (TPEA), or a styrene-basedelastomer (SBS), and the like. A mixture of these elastomers may beused. Embodiments of the method are particularly useful forethylene-α-olefin elastomers including difficult-to-disperse, non-polarelastomers such as EPM or EPDM, EBM, or EOM.

The method of making the CNT/carbon black preblend is to wet mix them ina suitable liquid. The mixing may be carried out in or with any suitablemixer, whether batch-wise or continuous, such as, for example, internalmixers, ribbon-blade batch mixers, high-shear batch mixers, single-screwextruders, and twin-screw extruders. The mixture may then be dried usingany suitable drying equipment, whether batch-wise or continuous, such asfor example, spray dryers, vacuum dryers, tray dryers, drum dryers,conveyor dryers, and the like. Filtering may be included in the dryingprocessing to concentrate the solids.

The preblended carbon nanostructures in preblend form may be added to apolymer or an elastomer composition according to known methods ofcompounding polymers, rubber and elastomers. For example, the rubber andits various ingredients may be compounded with the preblend using aninternal batch mixer, a single-screw extruder, a twin-screw extruder,two-roll mill, or the like. The various ingredients may be added instages, or all at once. Preferably, the compound is mixed in multiplestages if in a batch mixer.

The preblended carbon nanostructures comprising, e.g., carbon nanotubes,carbon black, graphitic carbon particles and or glassy carbon particlescan also be used in many other applications besides the incorporation ofsuch a preblend in an elastomer or other polymer. Such extendedapplications include among others, use of the preblends in batteryelectrodes, in particular lithium battery electrodes, batteryelectrolyte compositions, and in super capacitors.

The carbon preblend described above can be used as a conductive materialin a secondary battery as part of a battery electrode in variousproportions with an active material and a binder. Examples of commonactive materials that can be used in combination with the carbonpreblend are LiCoO₂, LiNiO₂, LiFeO₂, LiMnO₂, LiVO₂, or a combinationwhere a given transition metal ion (Co, Ni, Fe, Mn and V) is partiallysubstituted by other transition metal ions.

Without being limited by the choice of binders, common binders that canbe considered include polytetrafluoroethylene, polyvinylidene fluoride,polyethylene, polypropylene and synthetic rubbers among others.

For mixing of the dry form of carbon preblend with other kinds ofconductive, active, or electrolytic materials, for use for example inbattery electrolyte compositions, a wide range of solvents can be used.For example, propylene carbonate, ethylene carbonate, butylenecarbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonateand acetonitrile can be used alone or in combination with other solventsto form a slurry.

A thick film electrode can be formed on flexible polymeric substrates orpaper using a range of deposition techniques comprising doctor bladecoating, printing, rod coating or spray coating.

Taking advantage of the large surface area of CNT, the carbon preblendof the subject invention can also be used, for instance, as part ofelectrical double layer capacitors (commonly known as super capacitors),including use as electrolyte in combination with other forms of carbons,conductive materials, electrolytes, solvents and salts. One illustrativeexample of an electrolyte which might be used with the carbon preblendis acetonitrile used alone or in combination with a salt such astetraethylammonium tetrafluoroborate (C₂H₅)₄NBF₄.

As another example of use of the preblend form of carbon describedthroughout this specification in various details, the preblendcomposition can be applied on to various substrates in the form of apaint, coating, or slurry, or used as a component of a paint, coating,or slurry.

EXAMPLES

In the first example, a preblend including N550 carbon black and SWCNTis prepared to evaluate whether preblends of CNT can subsequently assistin the dispersion of the CNT in EPDM elastomer compositions.Single-walled carbon nanotubes (SWCNT) were provided by Nano-C, Inc. ofWestwood, Mass. As for the dimensions of the SWCNT, the diameter rangesfrom 0.8 to 1.9 nm with a higher abundance between 0.8 and 1.3 nm.Regarding the SWCNT bundle length, it ranges from 0.4 to 2 micrometer,most abundant from 0.5 to 1 micrometer. All other ingredients mentionedherein were obtained from commercial distributors and used as provided.

A first example blend of the single-walled carbon nanotubes with N550carbon black had a SWCNT content of 7.18% by weight, or 13:1 ratio ofcarbon black to CNT. This blend was prepared by first mixing the SWCNTin ethanol (1 gram of SWCNT in 35 ml of ethanol) and sonicating for 15minutes. Also, carbon black was dispersed in ethanol at a about 30 gm/land mixed with an IKA T25 disperser (sold under the IKA trademark by IKAWorks Inc.) for 15 minutes. The CNT solution was then added to anappropriate amount of carbon black solution and mixed with the IKA T25disperser for 15 more minutes. The solvent was then removed byfiltration and the carbon preblend material isolated and dried in a 60°C. oven overnight. This material was then characterized assessing thedegree of homogeneity and the identity of the resulting product.

Raman Spectroscopy results (as shown in FIG. 2) demonstrate the presenceof both of the ingredients in the blend and show very littlemodification in the peaks for each material. RBM- (≈200 to 300 cm⁻¹) andG- (around 1600 cm⁻¹) modes stem from the SWCNT, whereas the D-band(≈1300 to 1400 cm⁻¹) reflects the presence of carbon black. As thisobservation alone only shows the blend contains both materials but notthe detailed morphology, the blend was subsequently examined by SEMmicroscopy. SEM pictures of preblend material consisting of N550 carbonblack and SWCNT in a 13:1 ratio are shown in FIG. 3 includingmagnifications of: (FIG. 3A) 2500×, (FIG. 3B) 35,000×, and (FIG. 3C) and(FIG. 3D) 120,000×. FIG. 3A-3D shows a preblend material with uniquemorphology in which both constituent materials became intimately mixed.As the carbon black particles, used here, are much bigger than the widthof the nanotubes, the new material consists of nanotube network(s)surrounding carbon black particles, or, in other words, of a nanotubenetwork with carbon black particles dispersed therein. Evidence is foundthat this unique preblend structure provides improvements in subsequentdispersion of the nanotubes in an elastomer composition.

Other carbon-based particles consisting of graphitic, glassy orstructure-less carbon can be used as the carrier particulate solid ormixtures thereof, instead of or in addition to carbon black. Particleshape of the carrier can be regular or irregular.

Other fullerenic or nano-structured carbon materials such as spheroidalfullerenes (C₆₀, C₇₀, . . . , C₈₄, . . . ), graphenes, functionalized ornot, can be used instead of carbon nanotubes.

When the carbon-based carrier particles are larger than both the widthand length of the material with which they are mixed, a uniquecore-shell material in which nanotubes or other fullerenic materials(“the shell”) cover the surface of the graphitic, glassy orstructure-less “core.” Coverage may be up to 50% or 50 to 100%.

The diameter of the carbon-based or other particulate core material canbe between 20 nm and 20 μm while the longest dimension of the nanocarbonshell material can be between 0.7 nm and 2.0 μm.

An illustration of a core covered with carbon nanotubes as the shell isgiven in FIG. 4 in which polymer beads with diameters of approximately 1μm coated with single-walled carbon nanotubes are shown.

One final analysis of the preblended material was a measurement of theresistivity of the blend. The resistivity of the bulk materials waschecked and the preblend was nearly as conductive as the pure nanotubesthemselves, in spite of the low level of nanotubes in the preblend. Thissurprising result indicates the nanotube network may be expanded by theinterspersed larger carbon black particles without breaking the network.

The rubber compounding herein utilized a conventional B-Banbury labmixer with 1571 ml internal volume. In a first series of rubbercompounding examples, shown in Table 1, the control elastomercomposition was 100 parts by weight Vistalon 706 (EPM) sold under thattrade named by Exxon Chemicals; with 60 parts per hundred parts ofelastomer (“phr”) of N550 carbon black, and 5 phr of peroxide curative(Vul-Cup 40KE). The composition also included 0.3 phr of a retarder and1 phr of an antioxidant. This composition (Comp. Ex. 1) was mixed as thecontrol example (i.e., with no CNT). A second comparative example (Comp.Ex. 2) was mixed with 50 phr N550 and 3.87 phr of CNT, added into themixer together, but not as a preblend. Inventive example (Ex. 3) wasmixed using 53.87 phr of the aforementioned 7.18% preblend of SWCNT andcarbon black resulting in a CNT loading of 1.25 volume %. Cure studieswere run on a standard rubber moving die rheometer (“MDR”) at 170° C.(per ASTM D-5289). Tensile tests were carried out at room temperatureand 125° C. per ASTM D-412. Reported results include the “10% modulus”which is the stress at 10% strain in N/mm². Tests are at roomtemperature (“RT”) and in the with-grain (“w/g”) direction unlessotherwise indicated. Cross-grain tests are indicated as “x/g”. Theformulations and results are shown in Table 1. It can be seen thatmixing the SWCNT into the rubber composition produces the followingresults.

The MDR maximum torque observed at 170° C. (MH) was lower for both thesamples with carbon black and nanotubes. At the same time, the minimumtorque (ML) at this temperature was higher for the two samples withnanotubes than the control. The cure rate information on these compoundsis indicated by t90 in Table 1. The cure times for the compounds withnanotubes were significantly less than those of the control compound.This trend is consistent with that seen for the wax/carbon nanotubesdispersion evaluated previously in U.S. patent application Ser. No.14/243,634.

The Mooney viscosity (ML/132° C.) for these compounds (at a lowertemperature than the MDR) showed a small increase with the addition ofthe carbon nanotubes. There is essentially no difference in theviscosity for either route of incorporation of the nanotubes.

The dynamic modulus of the two compounds with nanotubes was determinedat 175° C. on the Rubber Process Analyzer (RPA) according to ASTMD-6601. Table 1 shows the same lower modulus (G′) for thenanotubes-containing compounds seen with the MDR. Here, when thenanotubes were pre-blended with carbon black, the resulting material wasslightly stiffer than simple addition of the two materials separately.This is an indication of some improvement in nanotubes dispersion usingthe carbon black/nanotubes blend. The small increase in modulus observedwith pre-blending the two materials is accompanied by an increase inhysteresis (tan 6), but only up to the level of the control.

Room temperature 10% modulus shows an increase in modulus with theintroduction of nanotubes into the compound and this is furtherincreased with the pre-blending of the two materials prior tocompounding. The largest increase in each case is in the with-graindirection and very slight in the cross-grain direction. At elevatedtemperature, the increase in modulus is marginal, following the trendindicated by the RPA and MDR data. There is no significant decline inmodulus over the control at high temperature, as was seen in previousstudies of wax/CNT predispersions. Thus, the method of preblending CNTwith carbon black provides more temperature stability than anothermethod.

Elongation at break shows a noticeable increase with introduction of CNTin the compound and an additional increase when the CNT are pre-blendedwith carbon black. This trend is consistent with or across the grain oforientation from processing. At elevated temperature (125° C.), thetrend is the same but the increases are all smaller than at RT.Toughness is also improved by CNT.

Tear properties (die-C tear strength according to ASTM D-624) show asteady increase with the addition of the CNT and further increase withthe pre-blending. Also, anisotropy is increased slightly with theintroduction of the CNT. Tear also is slightly increased over thecontrol at increased temperature.

The Shore A hardness for these compounds is essentially the same.

The DeMattia test was carried out in accordance with ASTM D-813 with apierced specimen. The cut growth rate is reported as the extrapolatednumber of mega-cycles to reach a 1-inch cut width, i.e., Mcycles/in.DeMattia crack growth rates showed a marked improvement regardless ofthe orientation, if any, of the CNT in the compound. This was evaluatedat 125° C., and the improvement occurs in spite of the fact that thereis some increase in stiffness of the compound.

The electrical properties of the compounds were evaluated using atwo-probe unit. Both samples with the CNT in the compound showedimproved conductivity, but there was no differentiation between the twosamples.

Finally, Field-emission SEM (FE-SEM) photomicrographs were taken of therubber samples for this series. FIGS. 5-7 show FE-SEM pictures at30,000× of three rubber compounds: FIG. 5 shows a control, carbon blackonly added to rubber; FIG. 6 shows separate addition to rubber of carbonblack and SWCNT; and FIG. 7 shows carbon black/SWCNT preblend preparedin liquid at Nano-C and added to rubber. The sample (FIG. 5) with carbonblack-only shows carbon black on the surface. The two samples with theCNT (FIGS. 6-7) show the carbon nanotubes interacting with the rubberand generating a web-like surface feature. On the basis of thesephotographs, it is believed the dispersion of the nanotubes was betterfor the Ex. 3 material than for Comp. Ex. 2.

The examples show that CNT preblended with carbon black can improverubber physical properties such as elongation at break, modulus, crackgrowth resistance and conductivity while other properties are unaffectedor slightly improved.

TABLE 1 Comp. Comp. Ex. 1 Ex. 2 Ex. 3 EPM 100 100 100 Carbon Black¹ 6050 0 ZDMA Coagent 15 15 15 Paraffin Oil 10 10 10 Antioxidant 1 1 1 SWCNT— 3.87 — CB/SWCNT Preblend — — 53.87 Retarder 0.3 0.3 0.3 Peroxide(40KE) 5 5 5 SWCNT (vol. %) 0 1.25 1.25 MDR-ML (lb-in) 1.99 2.16 2.42MDR-MH (lb-in) 31.2 26.7 27.8 MDR-t90 (min) 10.89 7.4 7.69 MV/132° C.(mu) 68.8 74.0 74.0 RPA-G′ (kPa)² 3867 2970 3405 RPA-tan δ² 0.142 0.0820.145 % Elong. at Break (RT) 296 390 403 10% Modulus (psi) (RT) 190.9210.3 220.0 Toughness (RT) 4328 5361 5886 Shore A Hardness 78 78 78 %Elong 125° C. 168.8 209.7 234.6 10% Mod. 125° C. (psi) 130.2 137.3 137.2Toughness 125° C 987 1126 1380 DeMattia 125° C. (Mcycle/in) 3.3 12501167 C-Tear x/g (lb/in) (RT) 290.1 373.8 391.5 C-Tear w/g (lb/in) (RT)292.9 358.7 371.3 ¹N550; ²1000 CPM, 0.18° strain, 175° C.

In the second series of examples, shown in Table 2, the same SWCNT asthe first example was used. In this example, however, a different liquidmedium was used to prepare two preblends of different ratios. Thesepreblends of CNT and carbon black were made using o-dichlorobenzene asthe organic liquid. The blends were prepared by first mixing the SWCNTin o-dicholorobenzene at a concentration of about 30 grams of SWCNT perliter of solvent with the IKA T25 mixer for 15 minutes. Then the carbonblack was mixed in o-dicholorobenzene for 25 minutes at a concentrationof about 20 to 30 grams per liter of solvent. Finally, appropriateamounts of the two mixtures were combined and stirred for about one hourwith the IKA T25 mixer. The solvent was then removed by filtration andthe remaining wet blend dried under vacuum at 70° C. for 48 hours. Inthis series, the effect of blend ratio and carbon black type areexplored. Two blend ratios were used in rubber formulations, 5:1 and13:1 carbon black to CNT. Two types of carbon black were used, N550 andN220, which differ primarily in particle size. SEM images of theresulting preblends prior to its use in a rubber formulation are givenin FIGS. 8-11. FIG. 8 and FIG. 9 show N220 carbon black/SWCNT preblendsat a 5:1 and 7:1 ratio, respectively at 40,000×. FIG. 10 and FIG. 11show N550 carbon black/SWCNT preblends at a 5:1 and 7:1 ratio,respectively, with FIGS. 10A and 11A at 25,000×, and FIGS. 10B and 11Bat 70,000×. The base EPM elastomer composition, the rubber mixing andthe testing were the same as for the first series. The rubberformulations used and the results are shown in Table 2 below.

Consistent with the inspection of the SEM images of FIGS. 3A-3D andFIGS. 8-11, the use of o-dicholorobenzene seems to provide a better endresult than the use of ethanol in the wet blending process. This can beseen, for example, by comparing the elongation at break for the Examples6, 7, and 10 in Table 2 versus the previous Ex. 3 in Table 1. Theo-dicholorobenzene blends give higher elongation, implying a toughercompound. The higher ratio of carbon black to CNT seems to give betterproperties than the lower ratio, suggesting better dispersion in theelastomer, perhaps due to the CNT network being more expanded by thecarbon black. The DeMattia crack growth data also showso-dicholorobenzene blends give even better results than the ethanolblends.

TABLE 2 Comp. Comp. Comp. Comp. Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex.10 EPM 100 100 100 100 100 100 100 N550 60 50 0 30.65 0 0 0 N220 0 0 0 060 50 30.65 ZDMA Coagent 15 15 15 15 15 15 15 Paraffin Oil 10 10 10 1010 10 10 Antioxidant 1 1 1 1 1 1 1 SWCNT — 3.87 — — — 3.87 — N550, 5:1CB:CNT — — — 23.22 — — — N550, 13:1 CB:CNT — — 53.87 — — — — N220, 5:1CB:CNT — — — — — — 23.22 Retarder 0.3 0.3 0.3 0.3 0.3 0.3 0.3 Peroxide(40KE) 5 5 5 5 5 5 5 SWCNT (vol. %) 0 1.25 1.25 1.25 0 1.25 1.25 MDR-ML(lb-in) 1.85 1.89 2.12 1.96 2.73 2.79 2.62 MDR-MH (lb-in) 32.51 25.824.89 23.42 32.36 26.88 26.33 MDR-t90 (min) 11.46 8.04 6.35 6.51 10.667.61 7.78 MV/132° C. (mu) 59.4 58.1 63.3 59.7 74.9 76.5 68.7 RPA-G′(kPa) 3513 2737 2740 2636 3903 3323 3159 RPA-tan δ 0.070 0.082 0.1020.104 0.098 0.117 0.110 Stress at Break (psi) (RT) 3179 3080 3154 34503977 3319 3859 % Elong. at Break (RT) 331.3 508.6 529.0 557.0 388.8481.6 509.4 10% Modulus (psi) 185.8 192.4 225.6 220.3 212.6 239.0 234.1Shore A Hardness 79 78 79 79 80 81 80 Stress at Break 125° C. 925 8251031 925 1221 961 1002 % Elong at break 125° C. 177.6 289.1 ~315 ~330212.8 ~305 ~420 10% Mod. 125° C. (psi) 114 97 84 98 108 103 102 DeMattia125° C. (Mcycle/in) 3.3 1200 1333 1333 28 700 783 C-Tear w/g (lb/in)(RT) 327 394 405 410 308 390 402 C-Tear w/g (lb/in) (125° C.) 117 133144 141 128 144 141

It should be noted that increased elongation at break for the examplecompounds along with significant improvement in 10% modulus, runscounter to the trends observed in the literature. For example, the Ex. 6and 7, which showed about 20% increase in 10% modulus, was accompaniedby a 60% increase in elongation at break. The CB/SWCNT combinations alsoshowed improvements in tear strength, cut growth rates on the DeMattiatest and fatigue resistance. The simultaneous improvement in modulus andelongation is believed attributable to improved dispersion of the CNT inthe elastomer composition, which is very difficult to quantify.Therefore, the invention may be characterized by the simultaneousincrease in modulus (e.g. 10% modulus) and elongation at break relativeto the same composition without CNT. Preferably, the increase in one orboth properties is in the range of at least 20%, or at least 30%, or atleast 50%.

It may also be noted conductivity of the rubber did not seem to bedependent on the method of dispersing the CNT, just on their presence insufficient amounts and the type of carbon black used. When the carbonblack used is not very conductive, we see a difference in theconductivity, favoring the solution blended CB/SWCNT over simple SWCNTaddition. When the carbon black is very conductive—i.e. N220—we see amuch smaller difference.

Thus, the present inventive method of dispersing CNT using a carbonblack/CNT preblend in elastomers results in improved dispersion overprior art methods, resulting in simultaneously increased modulus andelongation in the resulting elastomer composition. The inventiveelastomer compositions may be used to make various rubber articles, forexample, belts, hose, vibration control components, tires, sheet goods,and the like.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions, andalterations can be made herein without departing from the scope of theinvention as defined by the appended claims. Moreover, the scope of thepresent application is not intended to be limited to the particularembodiments of the process, machine, manufacture, composition of matter,means, methods, and steps described in the specification. As one ofordinary skill in the art will readily appreciate from the disclosure ofthe present invention, processes, machines, manufacture, compositions ofmatter, means, methods, or steps, presently existing or later to bedeveloped that perform substantially the same function or achievesubstantially the same result as the corresponding embodiments describedherein may be utilized according to the present invention. Accordingly,the appended claims are intended to include within their scope suchprocesses, machines, manufacture, compositions of matter, means,methods, or steps. The invention disclosed herein may suitably bepracticed in the absence of any element that is not specificallydisclosed herein.

1. A method for dispersing carbon nanostructures in a polymercomprising: wet-mixing in a liquid medium a blend comprising said carbonnanostructures and a particulate solid; drying said blend to form apreblend of the carbon nanostructures and the particulate suitable foradding to a polymer in a conventional compounding process; wherein saidpreblend forms a core-shell structure comprising a shell of said carbonnanostructures coating a core comprising a particle of said particulatesolid; and wherein said particular solid is selected from the groupconsisting of carbon black and polymer beads.
 2. The method of claim 1wherein said liquid medium is an organic liquid.
 3. The method of claim1 wherein said liquid medium comprises substituted aromatic molecules,alkyl substituted aromatics, halogenated substituted molecules,halogenated alkanes, partially hydrogenated aromatics, alkylamines,cyclic ethers, o-dichlorobenzene, xylene, benzene, dimethylformamide,ethylene chloride, chloroform, 1,2,4-trimethylbenzene,1,2,3,4-tetramethylbenzene, tetrahydrofuran, 1,2-dibromobenzene,1,1,2,2-tetrachloroethane, 1,2,3,4-tetrahydronapthalene, octadecylamine,acetone and mixtures thereof.
 4. The method of claim 1 wherein saidliquid medium is water or water stabilized by means of surfactant withsuch surfactant being at least one member selected from the groupconsisting of sodium cholate, sodium octylbenzene sulfonate, sodiumbutylbenzene sulfonate, sodium benzoate, sodium dodecyl sulfate,C₈H₁₇C₆H₄(OCH₂CH₂)n-OH wherein n˜10, dodecyltrimethylammonium bromide,dextrin, and polystyrene-polyethylene oxide diblock copolymer.
 5. Themethod of claim 1 wherein said particulate solid is carbon black.
 6. Themethod of claim 1 wherein the nano-structured carbon comprises carbonnanotubes (“CNT”), and wherein said preblend further comprises particlesof the particulate solid intermixed with a network of said CNT.
 7. Themethod of claim 6 wherein said CNT are single-wall carbon nanotubes. 8.The method of claim 6 wherein said CNT are multi-wall carbon nanotubes.9. The method of claim 1 further comprising mixing said preblend into apolymer composition.
 10. The method of claim 9 wherein the primarypolymer in the polymer composition is an ethylene-α-olefin elastomer.11. The method of claim 10 wherein the α-olefin of the ethylene-α-olefinelastomer is propylene, butylene or octene.
 12. The method of claim 9further comprising making a rubber article comprising said polymercomposition.
 13. The method of claim 12 wherein said rubber article is abelt, hose, tire, or vibration control component.
 14. A method fordispersing carbon nanotubes (“CNT”) in an elastomer comprising:obtaining a preblend of CNT and carbon black which was formed bywet-mixing the CNT and the carbon black in a liquid medium followed bydrying, wherein said preblend comprises a core-shell structurecomprising a shell of said CNT coating a core comprising said carbonblack; mixing said preblend into said elastomer with other ingredientsto form an elastomer composition.
 15. The method of claim 14 furthercomprising making an elastomeric article comprising said elastomercomposition.
 16. The method of claim 15 wherein said elastomeric articleis a belt, hose, tire, or vibration control component.
 17. The method ofclaim 15 wherein said elastomeric article is a power transmission belt.18. The method of claim 14 wherein the weight ratio of the carbon blackto the CNT in the preblend is in the range of 4:1 to 20:1.
 19. Themethod of claim 14 wherein the preblend further comprises particles ofthe carbon black intermixed within a network of the CNT.
 20. The methodof claim 14 wherein the preblend further comprises a nanotube networkwith carbon black particles dispersed therein.
 21. (canceled)
 22. Thepreblend composition of claim 25 wherein the preblend further comprisesa nanotube network with carbon black particles dispersed therein. 23.The preblend composition of claim 25 wherein the core particles arecarbon black particles and the carbon nanostructures are nanotubes. 24.(canceled)
 25. A preblend composition comprising carbon nanostructuresand a particulate solid, said preblend composition prepared bywet-mixing said carbon nanostructures and said particulate solid in aliquid medium, wherein the preblend composition comprises solid coreparticles of said particulate solid coated with a shell of said carbonnanostructures forming a core-shell material; and wherein the coreparticles are selected from the group consisting of carbon blackparticles and polymer beads.
 26. The preblend composition of claim 25wherein the core particles are regular or irregular in shape and have asize in the range of 20 nm to 20 μm in terms of average longestdimension.
 27. The preblend composition of claim 25 wherein the coreparticles are carbon black particles.
 28. The preblend composition ofclaim 25 wherein the carbon nanostructures consist of one or more fromthe group consisting of fullerenes, single-walled carbon nanotubes,multi-walled carbon nanotubes, and their chemical derivatives.
 29. Thepreblend composition of claim 25 wherein the shell coating on the coreparticles cover a surface area in the range of 50-100% of the totalsurface area of the core particles.
 30. A preblend compositioncomprising carbon nanostructures and a particulate solid, said preblendcomposition prepared by wet-mixing said carbon nanostructures and saidparticulate solid in a liquid medium followed by drying, wherein thepreblend composition comprises solid core particles of said particulatesolid coated with a shell of said carbon nanostructures forming acore-shell material; and wherein the core particles are selected fromthe group consisting of carbon black particles and polymer beadparticles.
 31. The preblend composition of claim 30 wherein the preblendfurther comprises a nanotube network with carbon black particlesdispersed therein.
 32. The preblend composition of claim 30 wherein thecore particles comprise carbon black particles and the carbonnanostructures comprise nanotubes.
 33. (canceled)
 34. The preblendcomposition of claim 30 wherein the core particles comprise polymer beadparticles.
 35. The core-shell material of claim 30 wherein the coreparticles are regular or irregular in shape and have a size in the rangeof 20 nm to 20 μm in terms of average longest dimension.
 36. Thecomposition of claim 30 wherein the core particles are carbon blackparticles.
 37. The composition of claim 30 wherein the carbonnanostructures consist of one or more from the group consisting offullerenes, single-walled carbon nanotubes, multi-walled carbonnanotubes, and their chemical derivatives.
 38. The core shell materialof claim 30 wherein the shell coating on the core particles cover asurface area in the range of 50-100% of the total surface area of thecore particles
 39. A method comprising: dispersing carbon nanostructuresin a liquid medium to form a dispersion; blending the dispersion with aparticulate solid to form a blend; and drying said blend to form apreblend; wherein the preblend comprises a core-shell materialcomprising a core of particles of said particulate solid coated with ashell of said carbon nanostructures; and wherein the particular solid isselected from the group consisting of carbon black and polymer beads.40. (canceled)
 41. (canceled)
 42. The method of claim 39 furthercomprising adding the preblend to a polymer in a compounding process.43. The method of claim 39 further comprising using the preblend as partof a battery electrode or as part of an electrolyte medium in a supercapacitor.
 44. The method of claim 39 further comprising using thepreblend in an electrolyte medium, paint, coating, or slurry.
 45. Themethod of claim 1 wherein said particulate solid is polymer beads. 46.The preblend composition of claim 25 wherein the core particles arepolymer beads.